AUTOMATIC CONTRAST COMPENSATION CIRCUIT

摘要

PURPOSE:To obtain a stabilized compensating picture signal with improved tracking performance to rapid change in the background density and light amount of an original, by performing compensating operation with a D/A converter in a sequential comparison A/D conversion circuit which execute A/D-conversion of the peak value of each line. CONSTITUTION:A picture signal VIN eliminating shading distortion is inputted and a peak value per one line is detected with a sampling section selecting circuit 2 and a peak value detection circuit 3. A picture signal input terminal 4 is connected to a reference voltage input terminal of a D/A converter 5 with an analog switch 6 at an original reading section and an output terminal of a reference voltage source 7 is connected to a reference voltage input terminal of the D/A converter 5 at a blanking section. A compensating coefficient corresponding to various values obtained by an output of a sequential comparison register 9 is stored in a memory 10 taking an output of the register 9 as an address input to constitute a compensation coefficient generating circuit.